Several forms of cytochrome P-450 are known to exist in mammalian liver. The type and amount of these "cytochromes P 450" present are affected by exposure of the animal to some drugs, polycyclic hydrocarbons, and other substances in the environment. Cytochrome P-450 is a major component of a mixed-function oxidase enzyme system which catalyzes the metabolism of many compounds including polycyclic hydrocarbons known to produce cancer in humans. The ability of the individual to activate or de-activate chemical carcinogens and thus his susceptibility to cancer induction by a given agent may depend on the absolute amounts or relative proportions of particular cytochrome P-450 species present. Hence, it would be useful to be able to recognize and quantitate the cytochrome P-450 forms. In this study methods for the identification of these proteins are being developed using rat and rabbit liver microsomes. These methods include 1) iso-electric focusing followed by enzymatic determination of mixed-function oxidase activity, 2) SDS-polyacrylamide gel electrophoresis, 3) spectrophotometric examination, and 4) immunological techniques. Once established, the methods will be used to analyze cytochromes P-450 of human monocytes and lymphocytes.